Fluidic stepping motor

ABSTRACT

A pneumatically operated motor which yields discrete steps of rotation. The motor comprises a stator, a fluidically or pneumatically energized nutator which drives a pin located therewithin and which, in turn, is eccentrically coupled to an output shaft. A plurality of ports are located in the stator which surrounds the nutator, and an equal number of sliding vanes serve to provide a plurality of expansible chambers surrounding the nutator. Air pressure is vented into one port and vented from the opposite port. This difference in pressure across the nutator produces a force on the pin eccentrically attached to the output shaft and causes the output shaft to rotate until the forces on the pin balance. By applying pressure at successive ports, the motor can be stepped along in finite degrees of rotation, with the extent of the step depending solely upon the number of ports and the spacing thereof. Fluidic circuitry is also provided for controlling the fluidic energization of the nutator in accordance with command information supplied to the motor.

llnited States atent John M. Rhoades Waynesboro, Va.

Feb. 27, 1969 Aug. 17, 1971 General Electric Company lnventor Appl. No. Filed Patented Assignee FLUIDIC STEPPING MOTOR 8 Claims, 8 Drawing Figs.

US. Cl

Int. Cl

Field of Search 123/8 PN;137/81.S;418/61- Primary Examiner-Martin P. Schwadron Attorneys-Joseph B. Forman, Gerald R. Woods, Frank L.

Neuhauser, Oscar B. Waddell and William S. Wolfe ABSTRACT: A pneumatically operated motor which yields discrete steps of rotation. The motor comprises a stator, a fluidically or pneumatically energized nutator which drives a pin located therewithin and which, in turn, is eccentrically coupled to an output shaft. A plurality of ports are located in the stator which surrounds the nutator, and an equal number of sliding vanes serve to provide a plurality of expansible chambers surrounding the nutator. Air pressure is vented into one port and vented from the opposite port. This difference in pressure across the nutator produces a force on the pin eccentrically attached to the output shaft and causes the output shaft to rotate until the forces on the pin balance. By applying pressure at successive ports, the motor can be stepped along in finite degrees of rotation, with the extent of the step depending solely upon the number of ports and the spacing thereof. Fluidic circuitry is also provided for controlling the fluidic energization of the nutator in accordance with command information supplied to the motor.

PATENIEU AUG! 7 |97| SHEEI 1 [IF 3 v INVENTOR. I JOHN M. RHOADES HIS ATTORNEY PATENIEDAIIBIYIBYI Y 3.600.115 sum 2 or 3 PULSE SOURCE l OSCILLATOR OSCILLATOR DIRECTION l 64 DISTANCE OOUNTER INVENTOR. INCREMEN A JOHN M. RHOADES HIS ATTORNEY PATENTED AUG] 719m SHEU 3 OF 3 INVILN'IOR. JOHN M. RHOADES HIS ATTORNEY lFLUlDIC STEPPING MOTOR BACKGROUND OF THE INVENTION This invention relates generally to expansible chamber motors, and more particularly, t6 pneumatic stepping motors.

Rotary expansion motors have been in use for many years. One common type of such motor operates on a sliding vane principle. This type of motor generally includes an expansion chamber which progressively expands from a gas inlet port to a gas outlet port. An eccentrically mounted rotor having radially outwardly extending vanes is located within this expansion chamber such that the vanes are resiliently urged against the walls of the expansion chamber to provide a complete seal between the wall and the vane. Depending upon the operation, the shaft of the rotor may be coupled to a drive shaft or to any power absorbing device for braking or driving.

In moving heavy loads such as machine tools, it is often desirable to accurately control the angle at which the shaft of a motor stops. This is especially true in numerically controlled machine tools where the positioning of the cutting head or some similar device is absolutely essential for correct operation of the tool. An improperly positioned cutting head would, of course, result in an improperly machined workpiece. At times, this can be very costly to a manufacturer. The abovedescribed pneumatic rotary motors, while they do provide an efficient power source, do not yield the desirable and necessary accuracy in positioning the shaft angle of the rotor shaft upon stoppage of the motor.

One solution to this problem is to utilize a stepping motor, i.e., a motor in which the revolution of the shaft takes place in finite steps. Stepping motors per se are known in the prior art; but, they generally operate on a piston basis which results in a limited travel of the output shaft. Some of these motors also operate only in one direction of rotation. This limited travel and single direction of rotation are undesirable, especially for use on numerically controlled machine tools.

SUMMARY OF THE INVENTION It is an object of this invention, therefore, to provide a pneumatic motor which will yielddiscrete steps of rotation.

It is a further object of this invention to provide such a motor which operates in either direction of rotation and which yields unlimited travel in either direction.

Briefly stated, the objects of this invention are achieved by providing a fluidically or pneumatically energized nutator which drives a pin located therewithin and which, in turn, is eccentrically coupled to an output shaft. The nutator is located within a stator or casing with which it cooperates to form a plurality of expansible chambers. The expansible chambers are connected through a plurality of ports located in the casing to a suitable source of pressurized air. By applying pressure at successive ports, the resulting expansion and contraction of the expansible chambers causes movement of the nutator which, in turn, causes rotation of the output shaft in finite degrees of rotation. The extent of rotation depends solely upon the number of ports and the spacing thereof. Fluidic circuitry is also provided for controlling the fluidic energization of the nutator in accordance with command information supplied to the motor.

BRIEF DESCRIPTION OF THE DRAWINGS While the specification concludes with claims particularly pointing out and distinctly claiming the subject matter which I regard as my invention, a preferred embodiment is disclosed in the following detailed description, taken in'connection with the accompanying drawing in which:

FIG. 1 is a perspective view showing a motor incorporating the teachings of the present invention;

FIG. 2 is an exploded view of the motor of FIG. 1;

FIG. 3 is a sectional view of the motor showing the nutator in one position;

FIG. 4 is a sectional view similar to FIG. 3 showing the nutator in a second position;

FIG. 5 is an exploded view of an alternative embodiment of this invention;

FIG. 6 is a perspective view, with one end plate removed, of a second alternative embodiment of this invention;

FIG. 7 is a diagrammatic sketch, in block diagram form, showing one possible control system utilizing the moto described in this invention; and

FIG. 8 is a second diagrammatic sketch, also in block diagram form, showing a more pneumatic control system utilizing a motor of this invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to the figures wherein like numerals represent like parts throughout, one example of a pneumatic stepping motor 10 is shown in FIGS. 1 and 2. The motor 10 comprises basically a stator 12, end plates 14 and 16 adapted to attach to opposite ends of the stator 12 such as by bolts 13, an output shaft 18, a pin 20 eccentrically connected to the output shaft 18 and formed as a part thereof, a nutator 22, and a plurality of sliding vanes 24.

The stator 12 comprises a generally cylindrical member with a circular opening 25 located throughout the entire length thereof. A plurality of input ports 26, equally spaced around the circumference of the stator 12, extend from the periphery of the stator 12 to the circular opening 25. These input ports 26 are connected by suitable hoses to a source of pressurized air (not shown) which is utilized to power the motor 10. The vanes 24 are located within a series of radial slots 28, equal in number to the number of input ports 26, and situated within the solid portion of the stator 12 as best shown in FIG. 2. The vanes 24 are free to slide within the slots 28, but are biased inwardly into sealing contact with the outer perimeter of the nutator 22 by some means such as springs 30.

The nutator 22 comprises a cylinder of a small enough diameter to fit within the circular opening 25 with sufficient clearance to permit both sideways and upwards movement thereof within the opening 25. The nutator 22 may be equipped with a plurality of longitudinal slots 32 equal in number to the number of vanes 24 to prevent rotation of the nutator 22 within the opening 25. The end of each vane 24 would then fit within the slot 32. A circular opening '34 is located at the center of the nutator 22 for receiving the pine 20, which is formed as part of the shaft 18, and which is eccentrically located with respect to the centerline of the shaft 18. The opening 34 is surrounded by a plurality of needle bearings 36 (FIG. 2) to facilitate the rotation of the pin 20 within the opening 34.

As best shown in FIG. 4, when the nutator 22 is positioned within the opening 25 of the stator 12, a plurality of expansion chambers 33 are formed. The boundaries of these expansion chambers 33 are the wall of the opening 25, the outer perimeter of the nutator 22, and the sides of a pair of the sliding vanes 24. The strength of the springs 30 would have to be sufficient, of course, to provide a pressure-type seal between the end of the vanes 24 and the outer periphery of the nutator 22. Each of the chambers 33 cooperates with one of the inlet ports 26 to allow pressurization or venting thereof.

OPERATION Operation of the motor 10 would be as follows. At a time when two of the inlet ports 26 (labeled 26a and 26b for clarity in FIG. 3) are pressurized, the two opposite ports 26c and 26d are vented. The pressure through the ports 26a and 26b, of course, causes expansion of the two expansion chambers labeled 33a and 33v in FIG. 3 and thus causes movement of the nutator 22 to the position shown in FIG. 3. The eccentric pin 20, located within the nutator 22, moves a corresponding distance. Thereafter, inlet ports 26b and 260 are pressurized, while ports 26a and 26d are vented. This causes expansion of the chambers 33v and 33w, and movement of the nutator 22 to the position shown in FIG. 4. The eccentric pin again moves with the nutator 22. As shown in FIG. 2, the eccentricity of the pin 20 with respect to the centerline of the shaft 18 will have caused the shaft 18 to rotate one-fourth turn clockwise as shown in FIG. 3. To rotate the shaft 18 onefourth turn farther, ports 26c and 26d are pressurized and ports 2a and 2612 are vented. As can readily be seen from the above description, the extent of each rotational step is directly determined by the number of inlet ports 26 located in the stator 12. For the four inlet ports shown in FIG. 3, the rotational step is one-fourth turn. If six inlet ports were substituted for the four shown, the rotational step would be one-sixth of a turn. The rotation of the shaft 18 could be reversed by merely reversing the direction of pressurization of the ports shown in FIG. 3. For example, for counterclockwise rotation, ports ad, dc, cb, ba, etc. are pressurized in that order.

As shown in FIG. 5, vanes 24 may slide within a plurality of slots located within a nutator 22', instead of within the stator 12 as shown in FIG. 2, while being biased outwardly into sealing contact with the outer extremities of the slots of stator 12 by some means such as spring 28. As the nutator nutates, the vanes slide in and out of the nutator slots while wobbling back and forth in the stator slots in the curved stator clearances 34 shown in the portion of the stator adjacent to the side of the vane. As is also shown in FIG. 5, a plurality of inlet ports 26 may be located within an end plate 14' rather than within the stator 12. Operation of this motor would be nearly identical to that described above. For counterclockwise rotation (as viewed from end plate 14') of the output shaft 18, ports ad, dc, cb, ba, etc. are pressurized in that order. For clockwise rotation of the output shaft 18', ports ab, be, cd, etc. are pressurized in that order.

Another alternative embodiment is shown in FIG. 6. In design, a nutator 22" may be formed from a deformable rubber member. A plurality of inlet ports 26" may again be located either within a stator 12" or within an end plate 14'. A plurality of needle bearings 36" surround an opening 34" located in the center of the nutator 22", and an eccentric pin 20" again fit within the central opening 34". A plurality of expansion chambers 33" are provided in cooperation with each of the inlet ports 26". The expansion chambers 33" are provided by means of a plurality of projections 42", extending radially from the periphery of the nutator 22", which fit within a corresponding number of longitudinal slots 40" formed within the stator 12" Operation of the motor is identical to that described above in that pressure developing in the expansible chamber causes the deformable nutator to deform around the inner wall of stator 12" to cause bearing 36" to undergo a nutating action. The chambers 33" are selectively pressurized through the ports 26". The nutator 22" must, of course, be made of a material sufficiently rigid enough to provide translation to the eccentric pin 20" upon expansion of one of the chambers 33". Choice of direction of rotation would again be determined by proper choice ofthe ports 26''.

It is possible to control the direction of rotation and the stepping rate of the output shaft 18 of any of the abovedescribed motors by applying two sources of air to the ports 26 with two fluidic or spool-type, four-way valves. Each of the valves pressurize one port 26 and vent the l80 displaced port 26. This means that two ports are pressurized and two ports are vented at all times. A sketch of a system utilizing this arrangement is shown in FIGS. 7 and 8. As shown most generally in FIG. 7, the two four-way valves 50 would be controlled by a directional control, labeled 52. The directional control 52 would, in turn, be governed by a pulse source 54 whose output frequency is indicative of the desired rotational speed of the motor It).

One possible example of the pulse source 54 which could be used is shown by a logic circuit schematically diagrammed in FIG. 8. An oscillator 56 provides a fixed frequency f to a frequency divider 58, which may be of any type, such as a pulse rate multiplier. The frequency divider 58 acts to modify the frequency f, to some output frequency f, which is a direct result of some programmed, desired speed provided to the frequency divider 58 by means of a tape input. In manual mode, a second fixed frequency oscillator 59 could provide a constant rotational speed to the output shaft 18 by operation of a switch 60.

A distance counter 62 provides the desired rotational distance of movement for the output shaft 18. The distance counter 62 could be a common variety, countdown type wherein the desired distance is input as a finite number of discrete steps. The counter 62 then registers each step until the counter reads zero. The desired frequency signal f, flows through an AND gate 63 which allows the signal to pass except when the distance counter 62 reads zero, i.e., except when the shaft 18 has rotated the desired distance.

A separate directional signal 64 provides the sole remaining signal to the directional control 52. With these two signals, the directional control 52 then regulates the pressurization of the four-way valves 50 for operation of the motor 10 as described above. This system is, of course, only a mere example of one of many systems which could be used to control the rate, direction, and distance of rotation for the output shaft 18 of the motor 10.

As can be seen from the above description, applicant has provided a pneumatic motor which yields discrete steps of rotation. The motor is completely reversible and provides unlimited travel in either direction. Applicant has also provided a motor in which the direction of rotation, the rate of rotation, and the total distance of rotation are easily controlled.

While the various features of the improved motor have been incorporated into a number of preferred embodiments, as described above, it should be obvious to one skilled in the art that certain changes could be made in these features without departing from the true spirit and scope of the invention sought to be covered in the appended claims.

What I claim as new and desire to be secured by Letters Patents of the U.S. is:

1. A pneumatic stepping motor comprising:

a. a hollow stator;

b. a nutator within said stator;

c. a plurality of slideable abutments located between said stator and said nutator adapted to provide a plurality of expansible chambers between said stator and said nutator;

d. a plurality of inlet ports located within said stator adapted to cooperate with said expansible chambers;

e. an opening located at the center of said nutator;

f. an output shaft;

g. a pin connected to said output shaft and located eccentrically with respect to the centerline of said shaft; and

h. said pin being positioned within said opening eccentrically with respect to the centerline of said nutator, means for rotating said pin about said centerline to drive said output shaft comprising means for successively pressurizing said inlet ports to pressurize said chamber, said nutator responsive to successive pressurization of said inlet ports to nutate and rotate said pin about said centerline, said means for successively pressurizing said inlet ports comprising a source of pulses of a first recurrence frequency, means for modifying the recurrence frequency of said pulses to derive pulses of a second frequency, a distance counter preset to a desired distance, said distance counter responsive to being counted down to select a portion of said second frequency pulses to provide a desired number of pulses of said second recurrence frequency, and means for successively pressurizing said inlet ports in accordance with said desired number of pulses of said second recurrence frequency.

2. The pneumatic motor of claim 1 wherein said stator comprises a first hollow cylinder, and said nutator comprises a second hollow cylinder.

3. The pneumatic stepping motor of claim 1 wherein said sealing means comprise a plurality of sliding vanes equal in number to, and spaced between the plurality of said input ports.

4. The pneumatic motor of claim 3 wherein said vanes slide within a plurality of grooves located within said stator.

5. The pneumatic motor of claim 3 wherein said vanes slide within a plurality of grooves located within said nutator.

6. A pneumatic stepping motor comprising:

a. a hollow stator;

b. a nutator within said stator;

c. a plurality of movable abutments located between said stator and said nutator adapted to provide a plurality of expansible chambers between said stator and said nutator;

d. a plurality of inlet ports located within said stator adapted to cooperate with said expansible chambers;

e. an opening located at the center of said nutator;

f. an output shaft;

g. a pin connected to said output shaft and located eccentrically with respect to the center line of said shaft; and

h. said pin being positioned within said opening eccentrically with respect to the centerline of said nutator, means for rotating said pin about said centerline to drive said output shaft comprising means for successively pressurizing said inlet ports to pressurize said chamber, said nutator responsive to successive pressurization of said inlet ports to nutate and rotate said pin about said centerline, said means for successively pressurizing said inlet ports comprising a source of pulses of a first recurrence frequency, means for modifying the recurrence frequency of said pulses to derive pulses of a second frequency, a distance counter preset to a desired distance, said distance counter responsive to being counted down to select a portion of said second frequency pulses to provide a desired number of pulses of said second recurrence frequency, and means for successively pressurizing said inlet ports in accordance with said desired number of pulses of said second recurrence frequency.

7. The pneumatic motor of claim 6 wherein said nutator comprises a deformable member.

8. The pneumatic motor of claim 6 wherein said abutments comprises a plurality of longitudinal grooves located within said stator, and a plurality of ribs projecting from said nutator which fit within said grooves. 

1. A pneumatic stepping motor comprising: a. a hollow stator; b. a nutator within said stator; c. a plurality of slideable abutments located between said stator and said nutator adapted to provide a plurality of expansible chambers between said stator and said nutator; d. a plurality of inlet ports located within said stator adapted to cooperate with said expansible chambers; e. an opening located at the center of said nutator; f. an output shaft; g. a pin connected to said output shaft and located eccentrically with respect to the centerline of said shaft; and h. said pin being positioned within said opening eccentrically with respect to the centerline of said nutator, means for rotating said pin about said centerline to drive said output shaft comprising means for successively pressurizing said inlet ports to pressurize said chamber, said nutator responsive to successive pressurization of said inlet ports to nutate and rotate said pin about said centerline, said means for successively pressurizing said inlet ports comprising a source of pulses of a first recurrence frequency, means for modifying the recurrence frequency of said pulses to derive pulses of a second frequency, a distance counter preset to a desired distance, said distance counter responsive to being counted down to select a portion of said second frequency pulses to provide a desired number of pulses of said second recurrence frequency, and means for successively pressurizing said inlet ports in accordance with said desired number of pulses of said second recurrence frequency.
 2. The pneumatic motor of claim 1 wherein said stator comprises a first hollow cylinder, and said nutator comprises a second hollow cylinder.
 3. The pneumatic stepping motor of claim 1 wherein said sealing means comprise a plurality of sliding vanes equal in number to, and spaced between the plurality of said input ports.
 4. The pneumatic motor of claim 3 wherein said vanes slide within a plurality of grooves located within said stator.
 5. The pneumatic motor of claim 3 wherein said vanes slide within a plurality of grooves located within said nutator.
 6. A pneumatic stepping motor comprising: a. a hollow stator; b. a nutator within said stator; c. a plurality of movable abutments located between said stator and said nutator adapted to provide a plurality of expansible chambers between said stator and said nutator; d. a plurality of inlet ports located within said stator adapted to cooperate with said expansible chambers; e. an opening located at the center of said nutator; f. an output shaft; g. a pin connected to said output shaft and located eccentrically with respect to the center line of said shaft; and h. said pin being positioned within said opening eccentrically with respect to the centerline of said nutator, means for rotating said pin about said centerline to drive said output shaft comprising means for successively pressurizing said inlet ports to pressurize said chamber, said nutator responsive to successive pressurization of said inlet ports to nutate and rotate said pin about said centerline, said means for successively pressurizing said inlet ports comprising a source of pulses of a first recurrence frequency, means for modifying the recurrence frequency of said pulses to derive pulses of a second frequency, a distance counter preset to a desired distance, said distance counter responsive to being counted down to select a portion of said second frequency pulses to provide a desired number of pulses of said second recurrence frequency, and means for successively pressurizing said inlet ports in accordance with said desired number of pulses of said second recurrence frequency.
 7. The pneumatic mOtor of claim 6 wherein said nutator comprises a deformable member.
 8. The pneumatic motor of claim 6 wherein said abutments comprises a plurality of longitudinal grooves located within said stator, and a plurality of ribs projecting from said nutator which fit within said grooves. 